Brainy Crows Finally Stumped by Intelligence Test

Maybe they’re not as smart as we thought: The New Caledonian crow, having passed so many other tests of animal cognition, has finally flunked an exam.

New Caledonian crows are valedictorians among corvids, a family of birds that includes ravens, jays and magpies. They’ve wowed scientists with their cognitive powers, even using wire as a food-fetching tool.

On one classic cognition test — retrieving a piece of food tied to a string — corvids perform so well that some researchers thought they didn’t just learn through rote trial and error, but envisioned problems in their head.

In a study published Feb. 22 in Public Library of Science ONE, researchers added a twist: They ran the string through a hole in a plywood platform. Crows could only see the food when directly above the hole. When they pulled back on the string, they’d lose sight of it. If they really did have a mental image of the task, it wouldn’t be a problem.

Twelve crows took the test: four who’d practiced on the old food-on-a-string setup, four who’d never seen it, and four who’d never seen it but could watch their reflection in a mirror.

Crows from the first group succeeded, but only after many attempts. Only one of the second group passed, also with difficulty. Two crows from the third group passed. It wasn’t the ace performance usually seen in crows.

“These results are not consistent with the hypothesis that the crows built a mental scenario,” wrote the researchers. “Our results raise the possibility that spontaneous string pulling in New Caledonian crows may not be based on insight but on operant conditioning mediated by a perceptual-motor feedback cycle.”

In other words, the crows relied on a simple trial-and-error approach. But the researchers did acknowledge that their sample size was limited, and that depth perception could be skewed in a confusing way by the experimental setup.

If nothing else, the crows did far better than finches. And even if they’re not good with spatial relationships, they’re certainly fast learners.

Images: 1) New Caledonian Crows on the old experimental setup at left, and on the new apparatus at right. Credit: University of Auckland. 2) Schematic of the new test design. Credit: University of Auckland.

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